1. Field of the Invention
The present invention relates to a liquid crystal display panel having an organic insulating film. More particularly, the present invention relates to a liquid crystal display panel that is adaptive for preventing liquid crystal contamination as well as improving an adhesive strength of a sealant and an organic insulating film, and a fabricating method thereof.
2. Description of the Related Art
A liquid crystal display device displays a picture by controlling the transmission of light through a liquid crystal by use of an electric field. A liquid crystal display device includes a liquid crystal display panel in which liquid crystal cells are arranged in a matrix shape, and a drive circuit to drive the liquid crystal display panel.
The liquid crystal display panel, as illustrated in FIG. 1, has a structure in which a thin film transistor substrate 2 and an upper plate 4 a disposed opposite each other and are bonded by a seal material 6. The bonded thin film transistor array substrate 2 maintains a fixed cell gap from the upper plate 4 by a spacer, and the cell gap is filled with the liquid crystal which is for controlling the transmission of light in accordance with an applied electric field.
The thin film transistor substrate 2 includes a gate line and a data line formed on a first substrate; a thin film transistor connected at a crossing of the gate line and the data line; a pixel electrode formed at each pixel area which is defined by the crossing of the gate line and the data line and connected to the thin film transistor; a passivation film to protect the structure; and an alignment film to align liquid crystal. The gate line receives a scan signal from a gate driver through a gate pad 10. The data line receives a video signal from a data driver through a data pad 8. The thin film transistor responds to the scan signal of the gate line to supply a video signal of the data line to the pixel electrode.
The upper plate 4 includes a color filter which is formed on a second substrate; a black matrix for dividing between the color filters and to reflect external incident light; a common electrode for supplying a reference voltage to the liquid crystal cells; and an alignment film to align liquid crystal.
The thin film transistor substrate 2 and the upper plate 4 are bonded together by a sealant 6 which is spread along the outer area of a picture display area where the liquid crystal cells are arranged. The upper plate 4 is bonded with the thin film transistor substrate 2 such that the gate pad 8 and the data pad 10, which are provided at a bordering area of the thin film transistor substrate 2, are exposed.
An inorganic insulating film or an organic insulating film is used for the passivation film which is included in the thin film transistor substrate 2 in the liquid crystal display panel. The inorganic insulating film is formed of an inorganic insulating material, such as SiNx, SiOx. The inorganic insulating film has a high dielectric constant and is formed by a deposition method. Accordingly, it has a disadvantage in that it is difficult to increase the height of the inorganic insulating film. Because of this, the pixel electrode and the data line, which have the inorganic insulating film disposed between them have to keep a fixed horizontal gap, e.g., a horizontal gap of 3˜5 μm, in order to minimize a coupling effect caused by a parasitic capacitance. As a result, the size of the pixel electrode which controls the aperture ratio of the liquid crystal cell is diminished, thereby lowering the aperture ratio.
An organic insulating film is applied in order to solve the low aperture ratio problem caused by the inorganic insulating film. As such, the organic insulating material has relatively low dielectric constant. Further, the organic insulating film has an advantage that it can be formed to be relatively thick by application methods such as spin coating. The presence of the organic insulating film, which has a relatively low dielectric constant and which can be formed relatively thick, reduces the capacitance of the parasitic capacitor between the data line and the pixel electrode. As a result, the pixel electrode can be formed to overlap the data line. As a result, the size of the pixel electrode is increased along with the aperture ratio.
An organic insulating film might also be applied to a structure in which the color filter is formed on the thin film transistor substrate, and a transflective structure in which each pixel area is divided into a transmission area and a reflection area.
According to the related art, the organic insulating film included in the thin film transistor substrate is in contact with the sealant, which is for bonding the thin film transistor substrate with the upper plate. The organic insulating film and the sealant, which is generally an epoxy resin have a weak adhesive characteristic such that its adhesive strength deteriorates over time. Deterioration of the organic insulating film provides a path through which the moisture of the outside penetrates due to its structure, resulting in defects such as a liquid crystal contamination. Further, at the interface where the organic insulating film and the sealant are in contact with the liquid crystal, liquid crystal contamination may be caused by the organic material with polarity which is generated by the mutual reaction of the polymer and monomer remaining behind at the organic insulating film and the sealant.